This invention relates to a conveyor sortation system and in particular to a positive displacement sortation system in which diverting shoes travelling with the conveyor surface laterally diverts packages onto selected spur lines.
Positive displacement sortation systems, such as the type disclosed in U.S. Pat. No. 4,738,347 for DIVERTER SHOE AND DIVERTING RAIL, issued to Gerald A. Brouwer and assigned to the present assignee, have long been known. Such a system includes a pair of endless chains and a plurality of slats connected at opposite ends to the chains in order to provide a moving conveyor surface. A diverting shoe is mounted to each slat in a manner that the shoe may glide across the slat. Movement of the shoes is effected by a guide pin and coaxial bearing, depending from the shoe, which engage a network of guide tracks beneath the conveying surface. At the loading end of the sortation system, the shoes all have a particular orientation to one side of the packages. When a package is to be diverted to a spur, a diverter switch is actuated to switch the guide pins for the shoes adjacent the package onto a diagonal track which causes the affected shoes to glide across the slats to divert the package.
The diverting motion applies reaction forces to the shoes tending to rotate the shoes about their vertical axis as well as about the long axis of the slats. These forces, of course, increase with heavier packages and those having a high coefficient of friction with the slats. These difficulties are aggravated by a desire to provide ever-increasing line speeds, which require greater ease of gliding between the shoe and the slats. Efforts to provide structural support to resist the reactive forces tend to be at odds with ease of glide.